Acquisition of one or more state variables relating to an air flow in an air system, for example a mass flow or a pressure, is necessary for the operation of an internal combustion engine. This variable is furnished to an engine control unit as a corresponding sensor signal.
Because of the regular opening and closing of the intake valves, however, pulsations occur in the flow of delivered fresh air in the air system of the internal combustion engine. Because of the offset interaction of the intake valves, the pulsations produced by the individual cylinders become superimposed, and form in the air system a pressure wave whose amplitude depends on the position of the throttle valve, the position of any exhaust gas recirculation valve, the geometry of conduits of the air system, and the engine speed.
The pulsation represents an interference variable in the state variable that is to be acquired, which is measured by sensors, for example the air mass sensor or pressure sensors, and is used in the engine control unit to control the internal combustion engine with the aid of actuators, for example the throttle valve of the exhaust gas recirculation valve, the wastegate valve, and the like.
Upon further processing of the state variable, as a rule the pulsation produced by engine operation is intended to remain out of consideration. State variables describing the air flow in the air system are therefore pre-processed by way of a digital filter concept in the engine control unit.